Bernard d



INTEROFFICE TRUNK CIRCUITS FOR TELEPHONE SYSTEMS May 24, 1927.

Original Filed June 18. 1920 Bernard D. M11 15 Reissued May 24, 1927. v,

UNITED ATES WARE.

'INTEBOFFICE TRUNK ciacurrs Ton TELEPHONE SYSTEMS.

Original no. 1,495,059, dated my 20, 1924, Serial No. 389,820, filed June 18, 1920.

reissue filed January 30,

My invention relates'in general to interofiice trunk circuits for telephone systems, but more especially to trunk circuits for l connecting automatic offices with manual ofiices in the same system, and the object of the invention is the. provision of an improved automatic to manual trunk circuit which is particularly useful for tem orarily connectingautomatic and manual 0 ces during a cut over from one system to the other, or for permanently connecting such oflices when automatic and'ma-nual systems serving the same territory are consolidated Q Trunk circuits of the above character are not broadly new, and the invention necessarily consists in certain principles of op- ,eration which are thought to be new, and in the various circuit. improvements employed for carrying out these principles; f

The invention will bedescribed with referenceto the accompanyingdrawing which is a circuit diagram of an interoflice' trunk circuit embodying the principles ofthe invention. I I

Referring to the drawing, the reference characters 30 and 31 indicate the two conductors of an inter-office trunk line. This trunk line extends from the so called re- I peater E which is located in an automatic oflice to an answering jack J at an A operators position in a manual ofiice, and is one of a group of similar trunk lines which are provided to handle the tra-flic from the automatie otlice to the manual oiiice. Another group of trunk lines, of a different type, is provided forhandling traffic in the other direction, but with these other trunks thepresent invention'is not concerned. In order to give the automatic subscribers access to. 'the trunk lines extending to the manual ofiice these trunkli'nes-are multipled in thebanlis of selector switches inthe' usual manner. Thus the trunk line shown in the drawing may be reached by way of bank contacts 2, 3, and 4, which may be located n the bank of a first selector switch, being connected in multiple to similar contacts in the-banks of the other firstfselectors in the automatic of- "fice. The automatic switches are of the well 'known Strowger vertical and rotary type, I operated according to the 'well known two wire system of control such as disclosed in v U. S. Patent No. 1,281,112, granted to B. D.

PATENT OFFICE.

BERNARD D. WILLIS, OF OAK PARK, ILLINOIS, ASSIGNOR, iBY IIESNE ASSIGNMENTS,

TO AUTOMATIC ELECTRIC INC OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- -therewith. This is in accordance with the usual practice'and is done primarily to avoid 'their functions and operations will be de- -to obtain connection with a subscriber in the manual oflice, and the process of setting the receir'er is removed the calling line is .tory, the first digit in each number being the 'sponding to the location of the linein the controlled to raise its shaft step by step which is reserved for the trunks extending ,to the desired manual office. At the end of Application for 1326. Serial No. 85,034.

lVillis, October 8, 1918, and the repeater E is provided to establish a holding circuit for any selector which is operated to establish connection with the trunk line associated the necessity of having three conductors between oflices.

As stated before, the answering jack J is located at an A operators position in the manual office. The particular A operator in front of whom this jack appears may handle trunked calls exclusively, or the jacks associated with the incoming trunks from the automatic ofiice may be distributed among a plurality of operators positions. In any case, the trunked calls are handledsubstantially like local calls originating in the manual office and the operator, or operators, have uniform supervision. Cord circuits such as disclosed in the fourth edition. of American Telephone Practice, on page 315, may be used. The group of relays indicated by the reference character-F. are the trunk relays, are located at the manual ofiice, and

scribed fully hereinafter.

- For this purpose it will be assumed that a subscriber in the automatic oflice desires up the connection will be described; When extended by means .of an individual line or trunk selecting switch to an idle first selector switch in the usual and well known manner. The manual subscribers may have full telephone numbers listed in the direcofiice digit, andthe remaining digits corremultiple at the manual oflice, and the calling subscriber will now operatehis calling de-- vice for the first digit in the desired number. By this means the first selector is dire'ctively until the wipers stand opposite the level the vertical movement ofthe selector the rotary trunk selecting movement is initiated automatically and the wipers are rotated step by step in search of an idle trunk line.

Assuming that the trunk line shown in the drawing is the first idle trunk line, when the wipers arrive at bank contacts 2, 3', and 4 the rotary movement willcease and by the operation of the switching relay in the selector the calling line will be extended by way of the selector line wipers, bank contacts 2 andL-and conductors 16 and 18 to ture, release trunk conductor 17, test contact 3, test wiper of the operated first selector, and the winding of the switching relay in said selector to battery. This circuit serves to maintain the selector in operated position during the call and it may be added that a branch of the above circuit performs the same function for the subscribers individual. line switch. It will be understood also that the ground potential on test contact 3 extends to multiple test contacts in the banks of other selector switches thereby rendering the trunk line busy.

The calling subscriber may now operate his calling device in accordance with the remaining digits of the desired number. As a result the line relay 5 is deenergized a plurality of times for each digit, but without effect, and the digits are wasted. The A operator at the manual exchange, however, has already been signaled. When relay 6 pulls up it closes a bridge across trunk conductors 3'0 and 31 which includes the right hand winding of induction coil R and the winding of relay 7. It follows that relay 7 will be energized in series with relays 33 and 3.4- at the manual exchange,the latter two relays'being bridged across the trunk line in series with the battery. Upon energizing, relay 7 grounds the holding circuit direct at its armature 13an'd thus cuts out the left hand winding of the induction coil R. At the manual exchange the relays 33 and 34 jointly close a circuit for the answering or call signal lamp L. At the same time relay 34 connects up a lead from the ringing machine RM. Condenser 51 is of very low capacity, preferably about .006 M. F., and permits just enough ringing current to leak back through the receiver at the calling station to give the calling subscriber the usual ringing current induction. This arrangement is customary in automaticsystems and is provided here for the sake of uniformity. Hearing the signal, the calling subscriber will understand that the desired line is being signalledand will wait on the line, although, as a matter of fact, the ringing machine has nothing to do with the signalling operation that has actually been performed.

When the operator sees the lighted answering lamp L, she will understand that a call has been received over the associated trunk line and will respond by plugging into the jack J with an idle cord-circuit. This lights the supervisory lamp in the cord circuit and energizes the sleeve relay 35. Relay 35, upon energizing, prepares a locking circuit for relay 36 at its armature i l, and at its armatures 43 and 45 disconnects relays 33 and 34 from the trunk line. This causes the answering lamp L to be extinguished, and

also disconnects the ringing machine RM. w

be denied inter-office service on that account has hisindividual line switch circuit so arranged that a. distinctive audible tone is placed on the holding circuit whenever a call is attempted. This tone is transferred to the line at the repeater E by means of the repeating coil R and when heard by the operator is suflicient authority for her to refuse to complete the connection. ence is made at this time to my U. S. Patent No. 1,281,112, granted Oct. 8, 1918, which shows and describes in full an arrangement of-this kind. In order to proceed with the explanation we will assume that no tone is heard by the operator when she comes in on the line, which means that the calling subscriber is entitled to service. The operator will therefore obtain the desired number from the calling subscriber and will pro- (feed to complete the connection with the other end of her cord circuit, either directly or with "the assistance of a'B operator, depending on the particular type of manual exchange in use. The connection having been established the operator will actuate key K momentarily and need pay no further attention to the'call, unless recalled by the supervisory signals in the cord.

When key K is operated a circuit is closed for relay 37 which. upon energizing, closes a circuit for relay '36 at armature 49. Upon energizing, relay 36 looks itself at armature 4:7 and at armature 46 prepares a circuit for relay 34:. In addition to closing the circuit Referof relay 36, rela 37 connects its upper winding in shunt condenser 52by means of its armature 48. Condenser 52 is included in the upper con'ductorof the trunk. line, normallypreventing currentflow from the cordcircuit; and it follows that when the condenser is shunted by the winding of relay 37, the said relay'will be locked up by-current flow over a circuit which includesthe battery at the cordcircuit and the relay 7 at the repeater E. Relay 7 is accordingly energized again to cut out the lefthand winding of induction coil R, and at the cord circuit the supervisory relay is energized to put out the supervisory lamp. It may be mentioned also that relay 7 disconnects the condenser which is normally bridged around its winding in order to give a-good circuit for the distinctive tone, when the tone is on the line.

The complete connection has now been established and when the called subscriber in the manual oflice answers the conversation can begin. 7

When the subscribers. are through talking they will both replace their receivers. When the called subscriber hangs up-the operator is given the usual disconnect supervision at the calling end of the cord circuit. When the calling subscriber hangs up the line relay at the repeater E is permanently deenergized and falls back to'break the circuit of theslow acting release relay 6. The latter relay then deenergizes also, the holding circuit is broken, and'the first selector and individual line switch are released. Relay 6 also opens the bridge across the trunk conductors and 31 at the repeater and relay 7 and the supervisory relay in thea-nswering end of the operators' cord circuit are deenergized. Thelatter relay permits the answering supervisory lamp to be lighted also and the operator now has a disconnect signal at both ends of her cord circuit.- At the same time that the supervisory relay falls back the relay 37 deenergizes and thereby disconnects its upper winding from'in shunt of condenser 52. Relay '36, however, re-

mains locked up. I

The operator may now pull down the connection and if she does so relays 35 and 36 willbe deenergized and all the apparatus will be in normal position. However, in order to complete the explanation, we will assume that another call is received over the same trunk line before the o rator has had time to disconnect. Sometimes, especially duringrush hou'rs,'the operators are rather slow at pulling down connections, and this may well occur. When the second calling subscriber connects with the trunk line the line and release relays 5 and 6 are energized as before and the bridge including relay 7 is closed across the trunk line at the outgoing side ofthe repeater E. As a result a circuit is closed for relay 34, which is now connected to the upper'line conductor by way of armatures 43, 46, and 48, for although relay33 is disconnected, the lower line conductor goes to battery at the manual exchange, nevertheless, because the cord is still up.

The superviso relay at the cord circuit is included in the lower talking strand, which goes to the ungrounded pole of battery and it follows that'relays 34 and 7 and the supervisory relay in the cord will be energized in series. This'puts out the supervisory lamp and removes one of the disconnect signals. Relay 34 being now operated the circuit of theanswering lampL .jack J for an insta:nt in order to deenergize relays 36 and 35. Whenthe plug is reinserted relay 35 will pull up again, but not relay 36, and relay '34, which falls back i when the plug is withdrawn, will remain deenergized. The circuitsare now in the same condition as they were in the casepreviously described, when the trunk ,line was first taken for use, and the operator will proceed according to the usual routine.

Although it is not essential, I have shown va test jack J which is provided for the convenience of'a switchboard man or other employee in .testing the trunk circuit. These test jacks may be mounted on the relay racks in the terminal room and afford ready access to the trunk circuits. \Vhen the jack J' is connected with, a telephone or other testing device is bridged across the two upper springs ofthe jack while the two lower springs are short circuited. 'The lat- -ter operation energizes relay 32 which pulls up and opens the two sides. of the trunk line, leaving the test telephone bridged across the line in the direction of the operator. The person testing can now talk to the operator and ascertain if the trunk line is working or not. Relay 32 also confnects the ungrounded pole of battery to the upper trunk conductor 30. Relay 6 at the repeater being at normal, relay 7 is now energized by current flow over the upper trunk conductor and at its armature 12 connects ground to the release trunk conductor 17. This renders the trunk line-busy.

too

It will be understood that if the trunk circuit should get out of order so that it would become necessary to establish a more permanent busy condition, the lower springs of-the' test jack can be short circuited bymeans of any-small metallic object which may be left in place until the circuit is repaired.

Having described my invention what I consider to be new and desire to have pro tected by Letters Patent will be pointed out in the appended claims.

What I claim as my invention is:

1. In a telephone system, a trunk line extending to an operators position, means whereby a calling subscriber can connect with said trunk line, a call signal at the operators position, means for operating said signal steadily when the call is received, means at the operators position for connecting said trunk line-with a called line, means whereby the calling .subscriber can disconnect from said trunk line, and means whereby it a second connection to said trunk line is established by a calling subscriber before the trunk line is disconnected from the called line the said call signal will be operated intermittently.

2. In a telephone system, a trunk circuit terminating in a jack at an operators position, means including automatic selectively movable switches whereby a calling subscriber can extend a connection to said trunk line, a call signal lamp at the operators position and means for causing the same to glow steadily when the connection to said trunk is established, means whereby the operator can connect said trunk line with a called line, means whereby the calling subscriber can release said switches, and means for flashing said call signal lamp in case a second calling subscriber should connect with said trunk line before means for disconnecting said second bridge when the operator plugs in to answer the call, a condenser in one conductor of said trunk line preventing current flow from the operators cord circuit, a relay in said first bridge which is deener-gized when the second bridge is cut off, a signalling device for indicating the character ofthe calling line connected in inductive relation to the trunk line to give the operator an audible signal when said second relay-falls back, and a key actuated'by the operator for short circuiting said condenser, Wihereby the said second relay is energized bycurrentfrom theoperators cord circuit and the said signalling device is rendered inoperative.

4. In a telephone system, a trunk line extending to an. operators position, means whereby a calling subscriber can connect with said trunk line, a call signal at the operators position, a pair of relays in said trunk line, means dependent upon the conent classes, an operators switchboard, a trunk line terminating m a jack on said switchboard, a cord circuitat said switch board, means including an automatic switch adapted to be set under the control of any calling subscriber for connecting such subscribers line to said trunk line, means automatically responsive to the insertion of the plug of said cordcircu-it in said jack for signalling the operatorover saidtrunk line,

to indicate the class of the calling line, said signalling means including a relay at the seized end of said trunk line for stopping the signalling operation, and a circuit controlled by the operator at said switch board for energizing said relay and maintaining the same energized to permit conversation with the calling subscriber.

6. In a telephone system, lines of different classes, an operators switch board, a

trunk line terminating in a jack on said switch board, a cord circuit at said switch board, means including an automatic switch adapted to be set under the control of any c-allingsubscr'iber for connecting such subscribers line to said trunk line, class signalling means associated with the seized end of said trunk line, means including a relay energized when the trunk is seized and automatic-ally deenergized responsive to the insertion of the cord circuit plug in said jack for rendering said signalling means effective to indicate the class of the calling line to the operator, andmeans controlled by the operator thereafter for v again energizing said relay to stop the signalling operation.

7. In a telephone system, lines of different classes, an operators switch board, a

trunk line terminating in a jack on said switchboard, a cord circult at said switch board, means including an auto-matlc switch adapted to be set under the control of any calling subscriber for connecting such subscr-ibe-rs line to said trunk. line, class signalling means associated with the seized end of said trunk'line, a battery bridged across said trunk line at .the switch board end thereof, a relay bridged across the seized end of said trunk line and responsive to current from said battery to render said signalling means ineffective, means for disconnecting said battery from in bridge of the trunk line responsive to the insertion of the cord circuit plug in said jack, thereby deenergizing said relay to permit said signalling means to become effective to indicate the class of the calling line tothe operator, and a circuit established thereafter under operator control for supplying cur rent to said relay from said cord circuit, whereby the relay is again energized to render the signalling means ineffective.

8. In a telephone system, a trunk line extending to an operators position, means whereby a calling subscriber can connect with said trunk line, a call signal at the operators position, means for operating said signal in one manner when the call is received, means at the operators position for connecting said trunk line with a called line, means whereby the calling subscriber can disconnect from said trunk line, and

means whereby if a second connection to said trunk line is established by a calling subscriber before the trunk line is disconnected from the called line the said call signal will be operated in a different manner.

9. In a telephone system, a called line lead- I ing to an operators position, a signal lamp on the called line at the'operators position,

meaiis'for initiating a call on the calling line whereby the lamp will responsively energize as a calling signal, means for responding to the call at the operators position and for controlled from the calling line' for reenergizing the lamp over a new circuit path regardless of the responded state of the called line being. maintained.

10. In atelephone system, a called line leading to a jack on an operators position, a calling signal device at the operators position, an answeringxcircuit at the operators position, a calling station, means for connecting the calling station to the called line to cause the callingsignal device to energize as a calling signal, means whereby thereupon connecting the answering circuit to the called line will complete a talking connection from and automatically deenergize the signal device, means' whereby the calling station can .disconnect from the called line without allectingthe calling signal device, and means "whereby reconnecting the calling station with the called line will cause the calling signal device to energize to indicate a new call regardless of the answering circuit having been maintained as primarily connected with the called line elements.

therebyldeenergizing the lamp, and means,

the calling station to the answering circuit,

11. In a telephone system, a called line.

leading to a jack on an operators position, a calling signal device on the operators position, an answering circuit at the operators position, a firstcalling station, a second call- 'ing station, means for connecting the first calling station to the called line to cause the calling signal device to energize as a calling signal, means whereby thereafter connecting the answering circuit to the ack will complete a talking connection from the first calling station to the answering circuit and automatically deenergize the signal device, means whereby the first calling station can disconnect from the called line without affecting the calling signal device nor the answering circuit connections associated with the jack, and means whereby connecting the second calling station with the called line will cause the calling signal device to energize to indicate a new call regardless of the answering circuit having been maintained connected with the called line.

12. In a telephone system, a called line leading to anoperators position, a signal lamp on the called line at the operators position, means controlled over the callin line for energizing the lamp as a calling signal, means for responding to the call at the operators position and for thereby deenergizing the lamp, and means controlled from the calling line for reenergizing the lamp as a calling signal regardless of the responded state of the called line being maintained,

means.

13. In a telephone system, a'called line leading to an operators position, a signal device'on the called line at the operators position, means controlled over the calling line for energizing the signal device as acalling signal, means for responding to the call at the operators positionand for thereby deenergizing the signal device, and means controlled from the calling line for reenergizing the signal device as a calling signal regardless of the responded state of the called line being maintained, without altering the state of the second said means.

14. In a telephone exchange system,the method which comprises extending a calling line and seizing an idle connectingcircuit in response to dialing impulses and in illumi- 'nating the lamp assigned to the selected connecting' circuit regardless of whether the 'switching terminal of said connecting cir- BERNARD n. WILLIS. 

